Mechanisms of the sparing effect of radiation dose fractionation (sdf) are investigated, using intact insects and insect cells in vitro. Special attention is paid to modification of kinetics of sdf by temperature, because insects are very amenable to temperature manipulation, and to evaluation of repair of noncytokinetic injury, which cannot be scored accurately in mammalian systems. Three manifestations of noncytokinetic injury are under study: Altered longevity in beetles; reduced sexual competitiveness in male beetles; and delayed pupation in diptera. The relative biological effectiveness (RBE) of densely ionizing particles for induction of these phenomena is also under study. BIBLIOGRAPHIC REFERENCES: Hagan, M.P. and H.S. Ducoff, Noncytokinetic injury: sparing effect of dose fractionation for delay of pupariation of the fleshfly, Sarcophaga bullata, Parker, Radiat. Res. 63, 378-381 (1975). Ducoff, H.S., Form of the increased longevity of Tribolium after X-irradiation, Exp. Geront. 10, 189-193 (1975).